Optical dispersion compensators are utilized to reduce amplitude distortion of received optical signals and thus increase the useable bandwidth of the optical signal. Dispersion compensators based on ring resonators may reduce amplitude distortion by over coupling (e.g., coupling coefficient (K) approaching 1) the signal received on a bus to the ring resonator in order to reduce the bandwidth limitations associated with a sharp resonance peak. In general, coupling to the bus must be greater than 90% for a planar ring resonator dispersion compensator (ring compensators) to be practical for dispersion compensation.
A ring compensator using a single directional coupler to couple the optical signals received on the bus to the ring resonator would require the directional coupler to have a coupling coefficient (k) equal to at least 90% to provide sufficient coupling for dispersion compensation. A ring compensator using a Mach-Zehnder interferometer (MZI) composed of two directional couplers with a means of tuning the optical path length of one of the arms between the couplers to allow arbitrary coupling between the bus and the ring resonator requires the directional couplers to have k in the range of 34% and 66%. However, the k of the directional couplers in planar optical circuits is highly dependent on process variables such as etch depth and sidewall angle.